1. Field of the Invention
This invention relates to a semiconductor light emitting device and, more particularly, to a semiconductor light emitting device using nitride III-V compound semiconductors.
2. Description of the Related Art
Known as semiconductor light emitting devices capable for emitting green to blue to ultraviolet light are those having light emitting diode structures in which nitride III-V compound semiconductors having wurtzite-structured crystalline structures, represented by gallium nitride (GaN), epitaxially grown on a sapphire substrate or a silicon carbide (SiC) substrate.
FIG. 1 shows a typical GaN light emitting diode having a conventional double heterostructure. As shown in FIG. 1, the conventional GaN light emitting diode includes a GaN buffer layer 102, n-type GaN layer 103, n-type AlGaN layer 104, GaInN light emitting layer 105, p-type AlGaN layer 106 and p-type GaN layer 107 which are stacked sequentially on a sapphire substrate 101. An upper lying part of the n-type GaN layer 103, n-type AlGaN layer 104, light emitting layer 105, p-type AlGaN layer 106 and p-type GaN layer 107 have a predetermined configuration defining an edge substantially normal to the substrate surface. These surfaces are covered with an insulation film 108 made of SiO.sub.2, for example, to protect these surfaces. The insulation film 108 has formed apertures 108a, 108b on the p-type GaN layer 107 and the n-type GaN layer 103, respectively. The p-side electrode 109 contact the p-type GaN layer 107 through the aperture 108a, and the n-side electrode 109 contacts the n-type GaN layer 108 through the aperture 108b.
Such GaN light emitting diodes are typically used in a mold-packed form using a resin as shown in FIG. 2 (for example, Japanese Patent Laid-Open Publication No. Hei 8-78727). That is, as shown in FIG. 2, in the mold-packed GaN light emitting diode, the sapphire substrate 101 of the GaN light emitting diode shown in FIG. 1 is bonded to the bottom surface of a depression 121a along the upper surface of a lead frame 121 with an adhesive 122. The bottom surface 121 and inner wall surfaces of the depression 121a serve as reflective surfaces for externally directing light departing from the light emitting layer 105 when the GaN light emitting diode operates. Used as the adhesive 122 is an epoxy resin adhesive. The p-side electrode 109 (not shown in FIG. 2) of the GaN light emitting diode is connected to the lead frame 121 by a wire 123, and the n-side electrode 110 (not shown in FIG. 2) is connected to a lead frame 125 by a wire 124. Then, the GaN light emitting diode is mold-packed together with adjacent parts of the lead frames 121, 125 in the resin 126 in a lens-shaped configuration for purposes of collecting light, among others.
However, conventional mold-packed GaN light emitting diodes are subject to deterioration with time, namely deterioration in luminance. A reason would be that the adhesive 122 is optically changed in color, or colored, due to an influence by light from the light emitting layer 104 of the GaN light emitting diode 105, and results in decreasing the transmittance and decreasing the intensity of light departing from the bottom surface of the sapphire substrate 101, passing through the adhesive 122, reflected by surfaces of the lead frame 121, and extracted to the exterior.